Size home battery storage against solar generation and self-consumption.
Battery capacity is bounded by whichever is smaller: the surplus solar available to store or the evening demand there is to serve. Oversizing beyond either leaves capacity permanently unused. The economics depend on the gap between import price and export payment, so batteries pay back fastest where export rates are lowest.
Battery Storage
Capacity = min(surplus solar, evening demand ÷ efficiency), with depth of discharge headroom
Capacity = min(surplus solar, evening demand ÷ efficiency), with depth of discharge headroom Battery capacity is bounded by whichever is smaller: the surplus solar available to store or the evening demand there is to serve. Oversizing beyond either leaves capacity permanently unused.
The economics depend on the gap between import price and export payment, so batteries pay back fastest where export rates are lowest.
This calculator takes 5 inputs: Daily electricity use, Daily solar generation, Share of use during daylight, Round trip efficiency, Import price per kWh. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.